Machkour, M., K. Afdel, and Y. I. Khamlichi. “Conversion Methodology from Hierarchical Model to Objectrelational Model With Structural and Semantic Aspects Preservation”. International Journal Of Mathematics And Computer Research, Vol. 2, no. 07, July 2014, pp. 503-11, https://ijmcr.in/index.php/ijmcr/article/view/156.